The technology of the present disclosure relates generally to distributed antenna systems (DASs) that support distributing communications services to remote antenna units, and particularly to measuring gain of DAS sub-systems within the DAS.
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, local area wireless services (e.g., so-called “wireless fidelity” or “WiFi” systems) and wide area wireless services are being deployed in many different types of areas (e.g., coffee shops, airports, libraries, etc.). Distributed communications or antenna systems communicate with wireless devices called “clients,” “client devices,” or “wireless client devices,” which must reside within the wireless range or “cell coverage area” in order to communicate with an access point device. Distributed antenna systems are particularly useful to be deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive radio-frequency (RF) signals from a source, such as a base station for example. Example applications where distributed antenna systems can be used to provide or enhance coverage for wireless services include public safety, cellular telephony, wireless local access networks (LANs), location tracking, and medical telemetry inside buildings and over campuses.
One approach to deploying a distributed antenna system involves the use of RF antenna coverage areas, also referred to as “antenna coverage areas.” Antenna coverage areas can be formed by remotely distributed antenna units, also referred to as remote units (RUs). The remote units each contain or are configured to couple to one or more antennas configured to support the desired frequency(ies) or polarization to provide the antenna coverage areas. Antenna coverage areas can have a radius in the range from a few meters up to twenty meters as an example. Combining a number of remote units creates an array of antenna coverage areas. Because the antenna coverage areas each cover small areas, there typically may be only a few users (clients) per antenna coverage area. This arrangement generates a uniform high quality signal enabling high throughput supporting the required capacity for the wireless system users.
As an example, FIG. 1 illustrates distribution of communications services to coverage areas 10(1)-10(N) of a DAS 12, wherein ‘N’ is the number of coverage areas. These communications services can include cellular services, wireless services such as RFID tracking, Wireless Fidelity (WiFi), local area network (LAN), WLAN, and combinations thereof, as examples. The coverage areas 10(1)-10(N) may be remotely located. In this regard, the remote coverage areas 10(1)-10(N) are created by and centered on remote antenna units 14(1)-14(N) connected to a central unit 16 (e.g., a head-end controller or head-end unit). The central unit 16 may be communicatively coupled to a base station 18. In this regard, the central unit 16 receives downlink communications signals 20D from the base station 18 to be distributed to the remote antenna units 14(1)-14(N). The remote antenna units 14(1)-14(N) are configured to receive downlink communications signals 20D from the central unit 16 over a communications medium 22 to be distributed to the respective coverage areas 10(1)-10(N) of the remote antenna units 14(1)-14(N). Each remote antenna unit 14(1)-14(N) may include an RF transmitter/receiver (not shown) and a respective antenna 24(1)-24(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 26 within their respective coverage areas 10(1)-10(N). The remote antenna units 14(1)-14(N) are also configured to receive uplink communications signals 20U from the client devices 26 in their respective coverage areas 10(1)-10(N) to be distributed to the base station 18. The size of a given coverage area 10(1)-10(N) is determined by the amount of RF power transmitted by the respective remote antenna unit 14(1)-14(N), the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the client device 26. Client devices 26 usually have a fixed RF receiver sensitivity, so that the above-mentioned properties of the remote antenna units 14(1)-14(N) mainly determine the size of their respective remote coverage areas 10(1)-10(N).
It may be desired to measure gain (i.e., attenuation) of the sub-systems of the DAS 12 in FIG. 1 to determine performance degradation. For example, the gain of the central unit 16 and/or the remote antenna unit 14, as DAS sub-systems, may be significantly different from their nominal gain level due to component variance, temperature changes, aging, and/or loading conditions. In this example, the central unit 16 and/or the remote antenna units 14(1)-14(N) may include an attenuator (not shown) that can be adjusted to adjust the actual gain back to the desired nominal gain level. In this regard, as an example, when the DAS 12 in FIG. 1 is first installed and all elements are interconnected and operated, it may be desired to measure the gain of each relevant DAS 12 segment. Corrective actions, such as gain adjustment, can be taken based on the measured gain of the DAS 12 segments. For example, the uplink gain of the remote antenna unit 14(2) in the DAS 12 in FIG. 1 may be measured by injecting a test signal Ts at an uplink input 28(2) and measuring the power of the test signal Ts at the uplink input 28(2) and an uplink output 30(2). So that the test signal Ts is provided in a frequency band that is supported for transmission in the remote antenna unit 14(2), the test signal Ts is provided in a common frequency band with the supported uplink communications signals 20U (i.e., a communications service signal). The uplink gain of the remote antenna unit 14(2) can be determined by subtracting the power of the test signal Ts at uplink input 28(2) from the power of the test signal Ts at the uplink output 30(2).
This method of gain measurement has a significant disadvantage. This method does not allow measuring gain of a DAS segment while the DAS is actively transferring communications service signals. The test signal, being in a common frequency band with a communications service signal, might interfere with the communications service signal. In addition, the communications service signal might disturb the test signal. A test signal in a different frequency band from the supported communications service signals may be employed for gain measurement to prevent the test signal from interfering communications service signals. However, in this scenario, the DAS segment would have to support the additional frequency band of the test signal and employ appropriate filters to filter the test signal from the communications service signals, thus adding additional cost and complexity to the DAS components in the DAS. However, because the gain of the DAS might be different at each frequency due to the frequency dependent response of the DAS components, an accurate gain measurement may only be possible using a test signal that has a frequency in a frequency band of a supported communications service signals in the DAS.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.